I have used stock F2 in valves in a K head.
Valve stem very soft, mushrooming very quick.
2 sets of IN valves in the 80's. Had to grind the top sides of stem to get valves out of the guides. I thought I had got a bad batch back then
After 3rd time 20 years later added lash caps on a new set that also added lenght so stem lenght as a K valve.
One thing is that the lash caps are soft. 0.25 mm dimple before 10.000 km.
Replaced that head a week ago
That head has a new set of 34mm SS valves I bought from CycleX. (Backcut done here, so ready to install)
TI retainer too. Just need to replace them. Will check lenght seal-keeper groove.
One more difference is the valve relief for keepers. F2 valves not long.
K valves longer than needed and risk for huge oil consumption with higher lifting cams if not using shorter guides or sunken stock guide where a new stopper groove is cut.
I have recently whitnessed the result when the keeper groove enter the guide seal. It became worse and worse, finally engine turned to an oilpump.
Got lack of oil on a ride. I checked oil and saw how it disappeared and stopped in time beside the road when oil tank was almost empty.
I called my wife, told her where in the garage I have oil and where I was waiting, 50km from home.
Engine did not smoke oil.
The lenght between seal and groove was 9.6mm, lift at running lash around 9.8mm. Higher rpm made it worse too.
That head got the guides redone and back into business a week ago.
